Patent Document 1 discloses a biological information measurement apparatus including a detection means including a light-emitting unit that emits light toward part of a biological body and a light-receiving unit that receives the light emitted from the light-emitting unit through the biological body, and a biological information display means that displays biological information on the basis of a detection result from the detection means. According to this biological information measurement apparatus, the detection means is configured such that the light-emitting unit and the light-receiving unit are parallel to a lengthwise direction of a subject's finger, a pulse wave signal is generated from light reflected by hemoglobin in the blood of the subject's finger and received by the light-receiving unit, and the biological information is obtained on the basis of the pulse wave signal.
Patent Document 2 discloses a pulse wave measurement apparatus in which a light-emitting element of a pulse wave sensor is configured to emit light toward a measurement area and extinguish the light in a periodic manner. This pulse wave measurement apparatus includes a light-emitting means that is repeatedly lit and extinguished, a light-receiving means that receives light reflected by or transmitted through the measurement area, and a pulse wave signal generating means that outputs a difference between a light reception signal during a lit period and a light reception signal during an extinguished period as the pulse wave signal. The pulse wave signal generating means includes a first sample holding means that samples and holds the light reception signal during the lit period and a second sample holding means that samples and holds the light reception signal during the extinguished period, and the stated pulse wave signal is outputted on the basis of a difference between the outputs of the two sample holding means.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-83914.
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2012-165851.
Improving SN ratios in pulse wave signal processing is an issue in biological information measurement apparatuses such as that disclosed in Patent Document 1. The biological information is obtained from a pulse wave component in the amplitude of detection light, and thus with detection light constituted of an AC component and a DC component, the AC is a component needed to obtain biological information such as a pulse wave signal, whereas the DC component is an unnecessary component. A higher ratio of the AC component to the total of the AC component and the DC component in the pulse wave signal, or in other words, a higher SN ratio, is therefore preferable for obtaining highly-accurate biological information. A configuration that improves the SN ratio of the pulse wave signal by controlling the light emission timing of the light-emitting means and the processing of the light reception signals, as per the pulse wave measurement apparatus disclosed in Patent Document 2, is problematic because the configuration complicates a control means and thus increases the cost of the apparatus. It is thus desirable to improve the SN ratio of the pulse wave signal by directly reducing the DC component of the detection light.